package P150;

public class P53 {
    /**
     * Definition for singly-linked list.
     * class ListNode {
     * int val;
     * ListNode next;
     * ListNode(int x) {
     * val = x;
     * next = null;
     * }
     * }
     */
    private static class ListNode {
        int      val;
        ListNode next;

        ListNode(int x) {
            val = x;
            next = null;
        }
    }

    public class Solution {
        public boolean hasCycle(ListNode head) {
            if (head == null || head.next == null) {
                return false;
            }
            ListNode slow = head;
            ListNode fast = head.next;
            while (slow != fast) {
                if(fast == null || fast.next == null) {
                    return false;
                }
                slow = slow.next;
                fast = fast.next.next;
            }
            return true;
        }
    }
}
